Update Register page to expose friendlier error

Assuming the libraries are doing their thing properly, `InvalidStateError` comes up most often when a user attempts to perform attestation with a credential they’ve already registered.

Unfortunately `InvalidStateError` as defined in the spec seems throwable under a few other circumstances, hence the vagueness of the error message here.

1 files changed, 7 insertions, 2 deletions

diff --git a/example/public/register/index.html b/example/public/register/index.html
index 05d7ef5..c8f0fa1 100644
--- a/example/public/register/index.html
+++ b/example/public/register/index.html
@@ -36,8 +36,13 @@
         try {
           attResp = await startAttestation(await resp.json());
         } catch (error) {
-          elemError.innerText = error;
-          throw new Error(error);
+          if (error.name === 'InvalidStateError') {
+            elemError.innerText = 'Error: Authenticator was probably already registered by user';
+          } else {
+            elemError.innerText = error;
+          }
+
+          throw error;
         }
 
         const verificationResp = await fetch('/verify-attestation', {